Photographic color developing compositions are used to process color photographic materials such as color photographic films and papers to provide the desired color images. Such compositions generally contain color developing agents, for example 4-amino-3-methyl-N-(.beta.-methane sulfonamidoethyl)aniline, as reducing agents to react with suitable color forming couplers to form the desired dyes. However, such color developing agents are susceptible to oxidation by dissolved oxygen. Therefore, an antioxidant is conventionally included in the color developer compositions to preserve the oxidation state of the color developing agent and thereby maintain useful color developer activity.
Color developing compositions also tend to include various metal ions, some of which can negatively affect the color developing agent by rendering it more unstable, and that can cause the formation of undesirable precipitates such as calcium precipitates. Thus, it has been common in recent decades to include sequestering agents to stabilize the compositions against precipitation of metal salts or hydroxides and against undesired decomposition reactions, such as the decomposition of hydroxylamine antioxidants to generate amines A variety of metal ion sequestering agents have been proposed for this purpose, including polyhydroxy compounds as described in U.S. Pat. No. 4,975,357 (Buongiorne et al), aminopolycarboxylic acids as described for example in U.S. Pat. No. 4,835,092 (Ishikawa et al), U.S. Pat. No. 4,837,132 (Fujimoto et al) and U.S. Pat. No. 4,906,554 (Ishikawa et al).
In addition, amino-N,N-dimethylenephosphonic acids, aminodiphosphonic acids, N-acylaminodiphosphonic acids, hydroxyalkylidene-diphosphonic acids and other polyphosphonic acids (including diethylenetriamine pentamethylenephosphonic acid) are described in U.S. Pat. No. 4,873,180 (Marchesano et al), U.S. Pat. No. 4,892,804 (Vincent et al) and U.S. Pat. No. 5,418,117 (Marsden) as useful sequestering agents in color developing compositions. However, as this art points out, such compounds are generally used in combination with lithium salts (such as lithium sulfate or a lithium salt of a sulfonated polystyrene) that provide lithium ions to control the formation of calcium precipitates with such sequestering agents (see U.S. Pat. No. 3,839,045 of Brown). In other instances, magnesium salts are added for the same purpose. Thus, the additional metal ions are used to solubilize the sequestering agent-calcium ion complex. One very common sequestering agent of this type that is used with lithium or magnesium ions is 1-hydroxyethylidene-1,1-diphosphonic acid that is described in U.S. Pat. No. 4,330,616 (Kurematsu et al). Without the lithium and/or magnesium ions, calcium sludge is often formed that requires additional maintenance and disposal.
However, if the level of calcium ion becomes too high, as may be the case with water in some locations, even the presence of lithium or magnesium ions will not prevent the formation of precipitates. Thus, there is a need to avoid the use of such sequestering agents, with or without lithium or magnesium ions. There is continuing efforts in the industry to provide improved and lower cost color developing compositions with improved stability and reduced precipitates.